1. Field of the Invention
This invention relates to refractive metamaterials and apparatus and methods that use such materials.
2. Discussion of the Related Art
Media having a negative refractive index are referred to as metamaterials. The refractive index has a negative sign when both dielectric constant, ∈, and magnetic permeability, μ, have negative real parts at a particular frequency. The negative refractive index causes electromagnetic radiation of the particular frequency to refract abnormally at interfaces between the metamaterial and media with positive refractive indexes. In abnormal refraction, incident and refracted light rays lie on the same side of the interface's normal in the incidence plane.
Metamaterials have been artificially constructed from spatially regular arrays of circuit elements. Some such artificial metamaterials include regular arrays of split ring resonators and wire strips as illustrated by FIGS. 1–4.
FIG. 1 shows a portion of one metamaterial that includes a slab 12. The slab 12 is formed by a 2-dimensional (2D) cubic lattice of rectangular fiberglass boards 14.
FIG. 2 shows a unit cell of the slab's 2D cubic lattice. The unit cell includes two fiberglass boards 14. The dimensions of the fiberglass boards 14 are: thickness of 0.25 millimeters (mm), length of 10 mm, and width of 5 mm.
FIG. 3 shows one of the fiberglass boards 14 of the unit cell. The fiberglass board 14 includes a wire strip 16 on a central axis of the backside of the board 14 and three split ring resonators (SRRs) 18 along the same central axis on the front side of the board 14. The wire strips 16 are formed of a 0.03 mm thick layer of copper. The other dimensions of the wire strips are: length of 10 mm and width of 0.25 mm.
FIG. 4 shows one SSR 18 of the fiberglass board 14. The SSR 18 includes two concentric split rings 20, 22 formed of 0.03 mm thick layers of copper. The dimensions characterizing the split rings 20, 22 are denoted as a, c, d, g, and w, and satisfy: c=0.25 mm, d=0.30 mm, g=0.46 mm, and w=2.62 mm.
In the exemplary metamaterial of FIGS. 1–4, the regular array of SRRs 18 produces the negative real part for μ, and the regular array of wire strips 16 produces the negative real part for ∈.